The diamond gem was on display as the 28-year-old actress arrived at the InStyle Summer Soiree with Annie Automatic musician Christopher.
Ashley chose a vibrant coloured dress which showed off her toned figure to wear to the event, while her rocker love chose a suit with a loosely knotted tie and a black leather jacket.
Eagle-eyed fans of the High School Musical star were given their first glimpse of her engagement ring earlier in the week. Stepping out with her new fiancé on Tuesday, Ashley debuted her sparkling new accessory.
Her representative confirmed the news of her engagement on Monday to People. On Thursday evening, Ashley telling tweeted, "Best night of my life. We're on top of the world" – a nod to Christopher's reported proposal on top of the Empire State building.
"Thank you guys for all your well wishes," she later wrote. "Means so much to me. We're so grateful and excited #imthehappiestgirlintheworld."
Ashley and Christopher made their first public appearance together in December 2012, when they visited the Apple Store in LA.
The musician is exactly her type. "She is in love with the 'darker, bad boy' types," a source told US Weekly. "And him being just that is why she has always been attracted to him.
"He's still a gentleman, though. He holds out her chair for her, holds the door etc, but is still edgy, which is why they mesh."